In wavelength division multiplex passive optical networks (WDM-PONs), each customer or optical network unit (ONU) communicates with the central office or optical line terminal (OLT) on a distinct wavelength. The wavelengths are combined via a multiplexing device which may be, for example, realized as an arrayed waveguide grating (AWG) in a remote node (RN), or via a distributed filter structure, before the WDM signal is sent to the OLT. To ensure proper combination in the multiplexing device, the center wavelengths of the optical channel signal which are generated in the ONUs need to be on a precise grid with a deviation of only few GHz. Furthermore, each ONU wavelength needs to match the port of the multiplexing device to which it is connected. For this purpose, the correct laser wavelength needs to be chosen. WDM transmitting devices which enable tuning of the center wavelength of the generated optical WDM channel signal are widely known. The tuning of the center wavelength may be enabled for only a rather small wavelength range which allows to correct small deviations of the center wavelength of the channel signal from the center wavelength of the respective channel transmission band. Further, WDM transmitting devices are known which enable wavelength tuning over a rather large spectral range, so such devices may be used to generate any required channel signal of a predetermined number of WDM channels.
It is at any rate desirable to enable the exact tuning of the center wavelength of a channel signal to the desired target wavelength, namely, the center wavelength of the predefined optical WDM channel. Generally, this center wavelength is predefined by the optical characteristics of the multiplexing device used to combine the plurality of optical channel signals.